Because of the ever increasing costs of energy, home heating costs, particularly in those parts of the country which experience cold winters, have risen astronomically. In addition, agricultural and industrial processes which require heat have become almost prohibitively expensive, especially for the small processor. Available heat-producing combustion units are either inefficient and do not yield a high percentage of usable heat or require expensive fuels such as oil to function efficiently. The most efficient units available are those which effect essentially complete combustion of the fuel, such as the stoves and furnaces disclosed in U.S. Pat. Nos. 843,105 to Roell, 1,668,585 to Custer, 1,717,657 to Box, 4,102,318 to Runquist and 4,182,304 to Mele. Ideally, the fuel is completely burned to produce only gaseous products of combustion, such as carbon dioxide, without the production of smoke. This requires a constant supply of oxygen to the combustion site. While many of the units disclosed in the aforementioned U.S. patents have made great strides toward completely gasifying the products of combustion, nonetheless, they continue to suffer from some significant disadvantages, especially when complete gasification of the combustion products is required so that the heat energy associated with these products can be used efficiently some distance from the combustion unit. In particular, all of the units disclosed in the aformentioned patents radiate a significant amount of heat into the immediate vicinity of the stove or furnace. Additionally, the heat loss around the burning chamber and the fuel feed opening experienced by prior art units considerably reduces the quantity of heat available for utilization downstream of the furnace or stove.
Moreover, although the prior art, specifically Mele in U.S. Pat. No. 4,182,304, discloses a combustion unit which burns a solid carbonaceous fuel like wood or coal more efficiently than earlier units, this increased efficiency is not necessarily realized with other solid biomass fuels, such as, for example, corn cobs or wood chips. Additionally, the Mele unit is intended to radiate sufficient heat to heat a given interior space to a comfortable temperature. Therefore, the combustion gases leaving the unit possess very little heat. In fact, since the sole function of the Mele unit, as well as that of the majority of the units disclosed in the U.S. patents cited hereinabove, is to radiate heat to the space around the unit, the combustion gases and products of combustion should ideally not possess any heat.
Consequently, a need exists for combustion unit which will efficiently burn a variety of solid biomass fuels, particularly those of low quality, so that complete combustion and gasification of these fuels takes place and a maximum amount of the heat produced by such combustion is made available for utilization in applications significantly downstream of the unit.